Strainer for a bilge pump

ABSTRACT

A straining device for a drainage pump, the straining device comprising a body defining an inner chamber; at least one straining element by which liquid may enter the chamber; and at least one outlet by which liquid may leave the chamber. The straining device further includes a liquid level sensor arranged to detect the level of a liquid in which said straining device is located during use and, upon determining that said liquid level exceeds a threshold, to cause an activation signal to be sent to said pump. The liquid level sensor comprises non-contact sensing means such as an electric field sensor. The sensor is located at the top of the straining device and arranged to project its sensing field upwardly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C.§371 of International Application No. PCT/EP2010/002067, filed Mar. 31,2010, which claims the benefit of Great Britain Application No.0905520.3, filed Mar. 31, 2009. Both of these applications are herebyincorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to strainers for use with pumps,especially bilge pumps.

BACKGROUND TO THE INVENTION

Strainers for bilge pumps, commonly known as strum boxes, are wellknown. Their purpose is to prevent debris being drawn from the bilge ofa vessel into the bilge pump. Traditionally, bilge pumps have beenmanually operated although, more recently, water level detectors,typically in the form of float switches, have been provided in the bilgearea of a vessel separately from the strum to control the operation ofpowered bilge pumps. However, the provision of a water level detectorincreases the complexity of installation since it has to be correctlypositioned in the bilge area with respect to the strainer. The waterlevel detector also adds to the cost of the bilge pump system.

It would be desirable to provide a system that overcomes the problemsoutlined above.

SUMMARY OF THE INVENTION

Accordingly, a first aspect of the invention provides a straining devicefor a pump, especially a bilge pump, the straining device comprising abody defining an inner chamber; at least one straining element by whichliquid may enter the chamber; and at least one outlet by which liquidmay leave the chamber, wherein the straining device further includes aliquid level sensor arranged to detect the level of a liquid in whichsaid straining device is located during use and, upon determining thatsaid liquid level exceeds a threshold, to cause an activation signal tobe sent to said pump.

Said liquid level sensor preferably comprises non-contact sensing means.Preferably, said liquid level sensor comprises at least one electricfield sensor. In preferred embodiments, the sensor may comprise anyconventional electromagnetic field sensor(s).

In preferred embodiments, said liquid level sensor is locatedsubstantially at the roof of said body, i.e. substantially at the top ofthe straining device. For example, said liquid level sensor may belocated inside said chamber on an inner surface of said roof.Alternatively, said liquid level sensor may be located on an externalsurface of said roof, in which case it is preferably located within asubstantially liquid-tight cover. Alternatively still, said liquid levelsensor may be incorporated into the body.

The preferred arrangement is such that the sensing field generated bysaid liquid level sensor extends upwardly in use. Any components of thesensing field that may otherwise have extended downwardly are preferablysuppressed or substantially eliminated. Laterally extending componentsof the sensing field may be present, although preferably only above thethreshold level. In general, the preferred arrangement is such that thesensing field (or at least the sensing field that is responsible foractivating the pump) exists only above said threshold. In preferredembodiments where the sensor is located at the roof, the arrangement issuch that the sensing field extends from the roof in a directionsubstantially away from the body.

Preferably, said liquid level sensor is arranged to cause saidactivation signal to be generated when the detected liquid levelindicates that said at least one outlet is substantially covered by saidliquid. In preferred embodiments, said at least one outlet is arrangedsuch that its top edge is substantially at or below the level of theroof. To this end, said at least one outlet is conveniently located in aside wall of said body.

Optionally, said liquid level sensor is arranged to cause a deactivationsignal to be sent to the pump upon detecting that the liquid level hasdropped below the threshold level. Alternatively, the sensor may bearranged to continuously or intermittently cause the activation signalto be sent until it determines that the liquid level has dropped belowthe threshold level, at which time the activation signal is terminated,termination of the activation signal being an indication that the pumpis to be deactivated.

Optionally, the sensor may be arranged to delay causing the activationsignal to be sent for a period of time until it has verified that theliquid threshold level has been exceeded, e.g. by establishing that aplurality of successive measurements indicate that the threshold isexceeded. Similarly, the sensor may be arranged to delay sending thedeactivation signal, or to delay terminating the activation signal, asappropriate, for a period of time until it has verified that the liquidthreshold level is not exceeded, e.g. by establishing that a pluralityof successive measurements indicate that the threshold is not exceeded.

A second aspect of the invention provides a pump system, especially abilge pump system comprising a straining device of the first aspect ofthe invention connected to a pump.

It is preferred that the pump is activated after a delay has elapsedfrom the time at which the sensor first detects that the liquid levelthreshold is exceeded when the pump is deactivated. This is convenientlyimplemented by a pump control system by, for example, configuring thecontrol system to delay activation of the pump for a period of timeafter having received an activation signal from the sensor and, at theend of the delay period, to activate the pump only if a deactivationsignal has not been received in the meantime, or if the activationsignal has not terminated in the meantime (depending on theactivation/deactivation protocol).

Similarly, it is preferred that the pump is deactivated after a delayhas elapsed from the time at which the sensor first detects that theliquid level has dropped below the threshold when the pump is activated.This is conveniently implemented by a pump control system by, forexample, configuring the control system to delay deactivation of thepump for a period of time after having received a deactivation signalfrom the sensor, or detected a termination of the activation signal,and, at the end of the delay period, to deactivate the pump only if anactivation signal has not been received in the meantime.

Further advantageous aspects of the invention will become apparent tothose ordinarily skilled in the art upon review of the followingdescription of specific embodiments and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are now described by way of example inwhich like numerals are used to indicate like parts and in which:

FIGS. 1A-1C are perspective views of a straining device embodying theinvention;

FIGS. 2A and 2B are perspective views of an upper body portion thestraining device of FIG. 1; and

FIG. 3 is a schematic view of the straining device of FIG. 1 in situ.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIGS. 1( a) to 1(c) and 2(a) to 2(b) of the drawings,there is shown, generally indicated as 10, a straining device, or strumbox, embodying the invention. The strum box 10 includes a hollow body,or housing, 12 shaped to define an inner chamber 14. The body 12includes a straining element 16 through which liquid, typically bilgewater, can be drawn into the chamber 14. In the illustrated embodiment,the straining element 16 comprises a plurality of apertures 18 formed ina wall, preferably the bottom wall, of the body 12. The strainingelement 16 is preferably removable, for example by means of a mechanicalinterference mechanism. This can best be seen from FIG. 1 C, which showsthe strainer 16 and upper body portion 13 in exploded view. The body 12defines an outlet 20 from the chamber 14 leading to a connector 22 forreceiving a drainage pipe (not shown in FIGS. 1( a) to 1(c) and 2(a) to2(b).

FIG. 3 shows a bilge pump system 30 incorporating the strum box 10. Thestrum box 10 is located in the bilge area 32 of a vessel 34 (of whichonly part of the hull is shown for illustration purposes). The system 30also includes a pump 36, in particular a bilge pump, which may take anysuitable conventional form. The pump 36 is a power-operated, e.g.electrically operated, pump as opposed to being manually operated. Adrainage pipe 38 is connected between the strum box 10 and the pump 36.A second drainage pipe 40 leads from the pump 36 to a drainagedestination, in this case the exterior of the vessel 34. It will be seenthat the pump 36 is remotely located with respect to the strum box 10,and therefore the bilge area 32, and as such is not submerged duringuse. The pump 36 is self-priming.

In use, when the pump 36 is switched on, it draws bilge water from thebilge area 32 through the strum box 10 and pipes 38, 40 and expels itoverboard. The straining element 16 removes debris from the bilge waterand so helps to prevent the pump 36 from becoming blocked.

The pump 36 preferably includes, or is connected to, a control system(not illustrated) for controlling the operation of the pump 36 inresponse to receiving one or more control signals. The control systemtypically comprises electrical and/or electronic circuitry for receivingcontrol signals and operating the pump 36 accordingly. Advantageously,the control system includes a programmable processor.

Referring again to FIGS. 1( a) to 1(c) and 2(a) to 2(b), the strum box10 further includes a liquid level sensor 50 for detecting the level ofwater around the strum box 10. Depending on the water level detected bythe sensor 50, the sensor 50 generates one or more control signals forcontrolling the operation of the pump 36. The control signals may becommunicated to the pump's control system by any suitable means, e.g. bya wired or wireless connection (not illustrated). In the preferredembodiment, the sensor 50 is arranged to detect whether or not the waterlevel meets a threshold level and, if so, to send a control signal toactivate the pump 36. If the detected water level is less than thethreshold, then the pump 36 is deactivated, or not activated, asapplicable. The sensor 50 may send a deactivating signal to the pump 36when it detects that the water level has dropped below the thresholdalthough, preferably, the pump 36 deactivates itself in the absence ofan activating signal from the sensor 50.

Advantageously, the sensor 50 is a non-contact sensor, i.e. it employsmeans for detecting the level of liquid without having to be in contactwith the liquid. In particular non-contact electromagnetic field sensorsare preferred, although other non-contact sensors such as RF (radiofrequency), capacitative, ultrasonic or magnetic sensors couldalternatively be used. In the preferred embodiment, the sensor 50 is anelectric field sensor comprising one or more electric field sensingelements.

The sensor 50 does not need to be located on the exterior of the strumbox 10 since its sensing element(s) do not need to be in contact withthe water. Conveniently, therefore, the sensor 50 is located on aninterior surface 52 of the body 12, preferably on the inside of the roof54 of the body, which in the illustrated embodiment is the roof of theupper body portion 13. In preferred embodiments, the roof 54 of the body12 corresponds with the roof of the chamber 14, although this need notnecessarily be the case. For example, in alternative embodiments, acompartment (not shown) may be provided above the chamber 14 (betweenthe chamber 14 and the roof 54) for housing, for example, electricalcomponents (optionally including the sensor 50). The sensor 50 could beinstalled at any suitable location in the body 12, for example on or inthe wall that divides the chamber 14 from the compartment, or even in aside wall of the body 12. It is preferred however, to provide the sensor50 substantially at, for example on or in, the in use uppermost surfaceof the body 12. Alternatively, the sensor 50 may be incorporated intothe body 12, preferably in the roof 54, or located inside or outside thebody 12, preferably on the roof 54, within a substantially liquid-tightcovering (not illustrated).

The sensor 50 generates a sensing field in use that allows the sensor 50to detect the presence or absence of a liquid, in this case water. Theposition and orientation of the sensor 50 affects the position andorientation of the sensing field and therefore affects the location ofthe threshold level for detecting water. When being used to detect arising water level (and so to cause the pump to be activated), it ispreferred that the sensor is arranged such that its sensing fieldextends, in use, generally upwardly such that there is substantially nosensing field below a horizontal threshold level. Depending on thenature of the sensor 50, the sensing field could for example besubstantially hemispherical or beam-like.

In the preferred embodiment where the sensor 15 is located substantiallyat the top of the body 15, the sensor 50 is positioned, and adapted ifnecessary, such that the electric field (not illustrated), or othersensing field e.g. electromagnetic or magnetic, that it generates duringuse extends in a direction substantially away from the strum box 10,i.e. upwards as viewed in FIG. 3. Ideally, any portion of the sensingfield that would otherwise extend in the opposite direction, i.e.downwardly, is substantially eliminated or at least suppressed to alevel that does not interfere with the operation of the system as hereindescribed. In general, the preferred arrangement is such that thesensing field (or at least the sensing field that is responsible foractivating the pump) exists only above said threshold. When the sensor50 is located at the roof 54, the bilge water impinges on the sensingfield only when the roof 54 is covered by the bilge water. When waterimpinges upon the sensing field, it interacts with the field in a mannerthat is detectable by the sensor 50. This causes the sensor 50 to sendan activation signal to the pump 36, or an output signal that causes anactivation signal to be sent. The sensor 50 may send a deactivationsignal to the pump 36 when the water level recedes such that the roof 54is no longer covered, or terminate the activation signal in cases wherethe absence of the activation signal is used as the deactivatingmechanism. It will be seen that the preferred arrangement is such thatsaid threshold level is substantially at the level of the top of thestrum box 10. It is advantageous to have the sensor 50 at the top of thestrum box 10 since this facilitates interaction between the water andthe sensor 50.

In preferred embodiments, the sensor 50 is positioned such that itsactivation signal is only generated when the strum outlet 20 is coveredby liquid. This ensures that the pump 36 does not suck air into the pumpsystem. In the illustrated embodiment, this aim is achieved by locatingthe sensor 50 at the roof 54 of the body 12 with its sensing field beingdirected upwardly, since the top of the outlet 20 is located at or belowthe level of the roof 54. For this reason, it is preferred that theoutlet 20 is located in a side wall of the body 54.

In use, the motion of the vessel 34 can cause bilge water to splash overthe strum box 10 even when the quiescent water level in the bilge area32 is not high enough to warrant turning on the pump 36. To avoid falseactivations of the bilge pump 36, it is preferred that the pump 36 isactivated after a delay has elapsed from the time at which the sensor 50first detects that water level threshold is exceeded when the pump 36 isdeactivated. This is conveniently implemented at the pump's controlsystem by, for example, configuring the control system to delayactivation of the pump 36 for a period of time after having received anactivation signal from the sensor 50 and, at the end of the delayperiod, to activate the pump 36 only if a deactivation signal has notbeen received in the meantime, or if the activation signal has notterminated in the meantime (depending on the activation/deactivationprotocol). For example a relatively short delay (e.g. 1 second) may beintroduced before activating the pump 36 and a longer delay (e.g. 15seconds) introduced before deactivating the pump 36.

Similarly, to avoid false deactivations of the bilge pump 36, it ispreferred that the pump 36 is deactivated after a delay has elapsed fromthe time at which the sensor 50 first detects that water level hasdropped below the threshold when the pump 36 is activated. This isconveniently implemented at the pump's control system by, for example,configuring the control system to delay deactivation of the pump 36 fora period of time after having received a deactivation signal from thesensor 50, or detected a termination of the activation signal, and, atthe end of the delay period, to deactivate the pump 36 only if anactivation signal has not been received in the meantime.

Alternatively, the delay may be implemented by the sensor 50. Forexample, the sensor 50 may be arranged to delay sending the activationsignal for a period of time until it has verified that the waterthreshold level has been exceeded, e.g. by establishing that a pluralityof successive measurements indicate that the threshold is exceeded.Similarly, the sensor 50 may be arranged to delay sending thedeactivation signal, or to delay terminating the activation signal, asappropriate, for a period of time until it has verified that the waterthreshold level is not exceeded, e.g. by establishing that a pluralityof successive measurements indicate that the threshold is not exceeded.

In alternative embodiments (not illustrated) a second sensor, which maysubstantially the same as the sensor 50, may be provided to deactivatethe pump 36 by generating a deactivating signal when the water level isdetermined to fall below a threshold level. The deactivating thresholdlevel is typically lower, in use, than the threshold level to which thesensor 50 operates. The deactivating sensor is preferably located in thebody 12, e.g. mounted on or in a wall of the body. A preferredarrangement is to mount the deactivating sensor directly or indirectlyto the ceiling of the body 12 by means of a spacer device such that itis lower, in use, than the sensor 50. The spacer device may for examplebe connected to the sensor 50. It is preferred that the threshold levelof the deactivating sensor is substantially at, or higher than (duringuse) the top of the outlet 20 to prevent air being sucked into the pump36. The preferred arrangement is such that the electromagnetic field, orother sensing field, of the deactivating sensor is directedsubstantially downwardly in use, although other arrangements arepossible.

The invention is not limited to the embodiments described herein, whichmay be modified or varied without departing from the scope of theinvention.

The invention claimed is:
 1. A straining device for a drainage pump, thestraining device comprising a body having a roof and defining an innerchamber; at least one straining element by which liquid may enter thechamber; and at least one outlet by which liquid may leave the chamber,wherein the straining device further includes a liquid level sensorarranged to detect the level of a liquid in which said straining deviceis located during use and, upon determining that said liquid levelexceeds a threshold, to cause an activation signal to be sent to saidpump, and wherein said liquid level sensor comprises non-contact sensingmeans, wherein said liquid level sensor is located substantially at saidroof and generates a directed sensing field in use, said liquid levelsensor being positioned so that, in use, said directed sensing fieldextends substantially upwardly from said roof and substantially none ofsaid directed sensing field extends below said threshold.
 2. A strainingdevice as claimed in claim 1, wherein said liquid level sensor islocated inside said chamber on an inner surface of said roof.
 3. Astraining device as claimed in claim 1, wherein said liquid level sensoris located on an external surface of said roof, preferably locatedwithin a substantially liquid-tight cover.
 4. A straining device asclaimed in claim 1, wherein said liquid level sensor is incorporatedinto the body.
 5. A straining device as claimed in claim 1, wherein saidliquid level sensor includes at least one first liquid level sensingelement that generates a sensing field in use, the arrangement beingsuch that the sensing field extends only substantially upwardly in use.6. A straining device as claimed in claim 1, wherein the liquid levelsensor is located at the roof, the arrangement being such that thesensing field extends generally upwardly from the roof in a directionsubstantially away from the body.
 7. A straining device as claimed inclaim 1, wherein said liquid level sensor is arranged to cause saidactivation signal to be generated when the detected liquid levelindicates that said at least one outlet is substantially covered by saidliquid.
 8. A straining device as claimed in claim 7, wherein said atleast one outlet is arranged such that its top edge is substantially ator below the level of the roof.
 9. A straining device as claimed inclaim 8, wherein said at least one outlet is located in a side wall ofsaid body.
 10. A straining device as claimed in claim 1, wherein saidliquid level sensor is arranged to cause said activation signal to begenerated when the detected liquid level indicates that said roof issubstantially covered by said liquid.
 11. A straining device as claimedin claim 1, wherein said liquid level sensor comprises at least oneelectric field sensor or at least one other electromagnetic fieldsensor.
 12. A straining device as claimed in claim 1, wherein saidliquid level sensor is arranged to cause a deactivation signal to besent to the pump upon detecting that the liquid level has dropped belowthe threshold level, or a second threshold level.
 13. A straining deviceas claimed in claim 12, wherein the liquid level sensor is arranged tocause said deactivation signal to be sent only after absence of saidliquid has been detected by said sensor at least twice within athreshold period of time.
 14. A straining device as claimed in claim 12,including at least one second liquid level sensing element thatgenerates a sensing field in use, the arrangement being such that thesensing field extends substantially downwardly in use, said deactivationsignal being dependent on the output of said at least one second liquidlevel sensing element.
 15. A straining device as claimed in claim 14,wherein said at least one second liquid level sensing element isarranged such that said second threshold level is substantially at thetop of said outlet, said second threshold level being below, in use,said threshold level.
 16. A straining device as claimed in claim 1,wherein the liquid level sensor is arranged to continuously orintermittently cause the activation signal to be sent until itdetermines that the liquid level has dropped below the threshold level,at which time the activation signal is caused to terminate, terminationof the activation signal being an indication that the pump is to bedeactivated.
 17. A straining device as claimed in claim 1, wherein theliquid level sensor is arranged to cause the activation signal to besent only after said liquid has been detected by said sensor at leasttwice within a threshold period of time.
 18. A straining device asclaimed in claim 1 wherein the liquid level sensor is arranged to causesaid activation signal to be terminated only after absence of saidliquid has been detected by said sensor at least twice within athreshold period of time.
 19. A straining device as claimed in claim 1,wherein said liquid level sensor is arranged such that said thresholdlevel is substantially at the level of a top of said body orsubstantially at the level of the top of said outlet.
 20. A pump systemcomprising a drainage pump with a pump control system and a strainingdevice, the straining device comprising a body having a roof anddefining an inner chamber; at least one straining element by whichliquid may enter the chamber; and at least one outlet by which liquidmay leave the chamber, wherein the straining device further includes aliquid level sensor arranged to detect the level of a liquid in whichsaid straining device is located during use and, upon determining thatsaid liquid level exceeds a threshold, to cause an activation signal tobe sent to said pump control system, and wherein said liquid levelsensor comprises non-contact sensing means, wherein said liquid levelsensor is located substantially at said roof and generates a directedsensing field in use, said liquid level sensor being positioned so that,in use, said directed sensing field extends substantially upwardly fromsaid roof and substantially none of said directed sensing field extendsbelow said threshold.
 21. The pump system of claim 20, wherein said pumpcontrol system is configured to deactivate said pump in response todetermining from said liquid level sensor that said liquid level doesnot exceed said threshold.
 22. The pump system of claim 21, wherein thecontrol system is arranged to delay deactivation of the pump for aperiod of time after having received a deactivation signal from thesensor, or detected a termination of the activation signal, and, at theend of the delay period, to deactivate the pump only if an activationsignal has not been received in the meantime.
 23. The pump system ofclaim 20, wherein said pump control system is arranged to delayactivation of the pump for a period of time after having received anactivation signal from the liquid level sensor and, at the end of thedelay period, to activate the pump only if a deactivation signal has notbeen received in the meantime.
 24. The pump system of claim 20, whereinsaid pump control system is arranged to delay activation of the pump fora period of time after having received an activation signal from theliquid level sensor and, at the end of the delay period, to activate thepump only if the activation signal has not terminated in the meantime.